This invention relates generally to an improved control mechanism for feeding limp sheet material, and particularly for such a system that guides fabric movement through a sewing machine.
Present clothing products often employ as an integral part of the design thereof extra stitching patterns for aesthetics or to form a trademark. One example of such trademark stitching is an arcuate back pocket stitching pattern that identifies the manufacturer of a leading brand of denim pants. In these and other controlled stitching applications, it is highly desirable that each item of clothing be made with substantially the same pattern and yet retain the appearance of being stitched under the control of a human operator. However, uniformity of stitching in a large volume clothing producing operation is difficult to maintain when the quality of the stitching is dependent upon the individual sewing machine operator's skill.
It has heretofore been proposed to use servo mechanisms, in some cases of the x-y type, to position the fabric work piece in correspondence with a pattern which is mechanically or electro-mechanically followed in synchronism with the sewing operation. See for example U.S. Pat. Nos. 3,385,244 -- Ramsey and 3,896,749 -- Brauns, et al.
These devices all suffer the disadvantage that their relatively large mass produces inertial forces which make for inaccurate stitching as well as greatly limiting the speed of the sewing operation. This is particularly true where stepper motors, or D.C. motors driven intermittently, are used to move the fabric work piece. Such motors simply cannot keep pace with a high speed sewing operation when they are required to move a fabric work piece fastened in a frame.
To overcome this problem, to some extent, other prior art devices have used guide wheels operated by servo motors which turn against the fabric work piece and guide it by pivoting it around the sewing needle during the interval when the needle is in the down position. See, for example, U.S. Pat. Nos. 3,459,145 -- Ramsey or 3,693,561 -- Hrinko, et al. Both of these devices use either stepper motors, or intermittently driven D.C. motors, and neither has a feedback, servosystem to follow an external pattern. Moreover both devices are greatly speed limited because of the high inertial forces needed to overcome their relative large masses.
In some of the above devices and in still other fabric feed guiding devices the guide mechanism is reciprocated up and down synchronously with the needle. See, for example, U.S. Pat. Nos. 3,650,229 -- Rovin and 3,693,561 -- Hrinko, et al. Such devices also are inherently speed limiting due to their need to overcome the inertia of their mass.
Therefore, it is a principal object of the present invention to provide a high speed automatic stitching pattern control system that can be operated with uniform results, even with the most complicated stitching pattern, by low skilled sewing machine operators.
It is another object of the present invention to provide an automatic stitching pattern control system capable of guiding cloth in a manner to stitch continuous curves.
It is yet another object of this invention to provide a mechanism for such automatic control that may be easily added to existing sewing machines.
It is a further object of the present invention to provide an economical and simple automatic stitching pattern control system wherein a controlling pattern may easily be generated and duplicated.
It is still another object of the present invention to provide an automatic stitching pattern control system that is easily integrated into a continuous process clothing manufacuturing operation.